The invention relates to a process for removing alkali and alkaline earth metals from aluminum melts by introducing aluminum fluoride powder into the melt.
Primary aluminum from the electrolytic cell often contains considerable amounts of alkali and alkaline earth metals. Before such contaminated metal can be processed further, in particular before casting into rolling slabs, it is in most cases essential that the concentration of the undesired impurity elements is reduced.
Known from the European patent publication EP-A-0 065 854 is a process for removing alkali and alkaline earth metals from aluminum melts, said process involving the addition of aluminum fluoride powder to a vortex created in the melt. The treatment takes place in a cylindrical container having a capacity for 3-5 tons of molten aluminum. This process enables small charges of aluminum to be treated effectively in a relatively short time. On the other hand, the amount of aluminum fluoride required to treat each ton of metal is very high. Furthermore, special devices are required to stir the melt.
In view of the above the object of the invention is to develop a process of the kind described at the start, by means of which the consumption of aluminum fluoride is kept as low as possible, at the same time maintaining the high efficiency of melt purification. In addition it is a further object to be able to carry out the process using already existing melt treatment equipment without very much alteration to the same.